In some methods of extracorporeal blood treatment, substituate liquid is supplied to the utilized extracorporeal blood circuit and/or a blood treatment module, e.g., the blood filter. Determining the size of such substituate flow or other volume flows is not reliably possible under practical conditions.
One object of the present invention is an improved method for determining a volume flow in a blood treatment apparatus. Furthermore, a suitable calculating device, a corresponding blood treatment apparatus as well as a digital storage medium, a computer program product and a computer program are specified.
According to the present invention, a method for determining at least a first volume flow in a blood treatment apparatus is proposed. The blood treatment apparatus comprises: a primary circuit for conducting the blood to be treated, a secondary circuit for conducting a fluid that is used for the blood treatment, and a blood treatment module as a section of the primary circuit and/or of the secondary circuit which is provided for exchanging fluids and/or substances between the primary circuit and the secondary circuit. The blood treatment apparatus may optionally comprise a fluid connection between the primary circuit and the secondary circuit, provided for introducing the first volume flow from the secondary circuit into the primary circuit.
The method encompasses determining the first volume flow of the secondary circuit taking into account a first pressure measurement and a second pressure measurement in the secondary circuit. Alternatively or additionally, the method may encompass determining a volume flow of the secondary circuit upstream from the blood treatment module taking into account or considering a first pressure difference, and/or determining a volume flow of the secondary circuit downstream from the blood treatment module taking into account or considering a second pressure difference.
The calculating device according to the present invention is provided and/or programmed for executing the method according to the present invention.
The blood treatment apparatus according to the present invention is provided for extracorporeally treating blood. It is further embodied and provided for executing or performing the method according to the present invention. It comprises at least or is connected herewith: a calculating device according to the present invention, a primary circuit for conducting the blood to be treated, a secondary circuit for conducting a fluid that is used for the blood treatment, a blood treatment module as a section of the primary circuit and/or of the secondary circuit, which is provided for exchanging fluids and/or substances between the primary circuit and the secondary circuit, and a fluid connection between the primary circuit and the secondary circuit, provided for introducing the first volume flow from the secondary circuit into the primary circuit.
All advantages resulting from the method according to the present invention may in certain embodiments according to the present invention undiminishedly also be achieved by use of any of the subjects according to the present invention. In some embodiments according to the present invention, this also applies for the digital storage medium according to the present invention, the computer program product according to the present invention and the computer program according to the present invention.
A digital, particularly a non-volatile storage medium according to the present invention, particularly in the form of a machine-readable data storage device, particularly in the form of a disk, CD, DVD or EPROM, particularly with electronically or optically readable control signals, may interact with a programmable computer system such that the mechanical steps of a method according to the present invention are prompted.
Hereby, all, several or some of the mechanically executed steps of the method according to the present invention may be prompted.
A computer program product according to the present invention comprises a program code stored on a machine-readable data storage device for prompting the mechanical steps of the method according to the present invention when the computer program product runs on a computer. According to the present invention a computer program product can be understood as, for example, a computer program which is stored on a storage device, an embedded system as a comprehensive system with a computer program (e.g. an electronic device with a computer program), a network of computer-implemented computer programs (e.g. a client-server system, a cloud computing system, etc.), or a computer on which a computer product is loaded, executed, saved or developed.
A machine-readable data storage device denotes in certain embodiments of the present invention a medium that contains data or information which is interpretable by software and/or hardware. The medium may be a disk, a CD, DVD, a USB stick, a flash card, an SD card or the like.
A computer program according to the present invention comprises a program code for prompting the mechanical steps of a method according to the present invention when the computer program runs on a computer. A computer program according to the present invention can be understood as, for example, a physical software product, which is ready for distribution and contains a computer program.
It also applies for the computer program product according to the present invention and the computer program according to the present invention that all, several or some of the mechanically executed steps of the method according to the present invention are prompted.
Embodiments according to the present invention may comprise one or more of the features named hereafter. Additionally, embodiments according to the present invention are the subject of the dependent claims.
In all of the following embodiments, the use of the expression “may be” or “may have” and so on, is to be understood synonymously with “preferably is” or “preferably has,” respectively, and so on, and is intended to illustrate certain embodimentts according to the present invention.
In some embodiments according to the present invention, the primary circuit and/or the secondary circuit is a closed circuit. In other embodiments according to the present invention, the primary circuit and/or the secondary circuit is an open circuit or a non-closed circuit.
In some embodiments according to the present invention, the secondary circuit is a dialysate circuit. In other embodiments according to the present invention, it is not a dialysate circuit.
In certain embodiments according to the present invention, a volume flow is a flow rate.
In some embodiments according to the present invention, the first volume flow is a substituate flow.
In some embodiments according to the present invention, the first volume flow is an ultrafiltration flow.
In some embodiments according to the present invention, “determining” stands for quantitative determining. In other embodiments according to the present invention, “determining” stands for qualitative determining. The latter may, e.g., be or encompass specifying the first volume flow as a proportion of a second volume flow or a total volume flow.
In some embodiments according to the present invention, the first pressure measurement and the second pressure measurement are or will be measured at different measuring points within the secondary circuit.
In some embodiments according to the present invention, the first pressure difference and the second pressure difference relate to pressure differences within the secondary circuit.
In some embodiments according to the present invention, the first measuring point is located upstream from each blood treatment module, e.g., upstream from each dialysis filter, and the second measuring point is located downstream from each blood treatment module, e.g., downstream from each dialysis filter. If the section of the dialysis filter encompasses several dialysis filters that are separate from each other, they may in some embodiments according to the present invention be considered as a joint dialysis filter.
In some embodiments according to the present invention, the pressure sensors do not serve to determine the respective filtrate flow or another flow through the membrane of a blood treatment filter.
In certain embodiments according to the present invention, the first pressure measurement indicates a pressure in the secondary circuit at a first pressure measurement point upstream from the blood treatment module, namely downstream from a split, separation or junction of the first volume flow from a second—preferably larger—volume flow.
In some embodiments according to the present invention, the volume flow is split in a dialyzing liquid filter or an online filter. An online filter may be a filter in which the amount of liquid the dialysis machine needs or allows for substitution, and which is taken from the closed system before the dialyzer, is filtered again.
In some embodiments according to the present invention, the second pressure measurement specifies a pressure in the secondary circuit at a second pressure measurement location, which is located downstream from the blood treatment module.
In some embodiments according to the present invention, the first volume flow branches off a second volume flow and/or is a partial flow of the second volume flow. In certain embodiments according to the present invention, the first volume flow is taken from the second volume flow by use of a pump, e.g., by use of a substituate pump, and conveyed into the primary circuit or into the blood treatment module.
In some embodiments according to the present invention of the method, a flow resistance between the first pressure measurement location and the second pressure measurement location is determined as a function of the second volume flow and the difference between second pressure measurement and first pressure measurement.
In some embodiments according to the present invention, the function of the flow resistance is linearized in the area of at least one operating point.
An operating point may be specified by use of a volume flow and a pressure difference. A linearization is given, e.g., when adjacent operating points in a predefined volume flow area/pressure difference area are located on a straight line that may be mathematically described. The correlation of the measuring points with the straight line may be specified by use of the correlation coefficient R2. A sufficiently accurate linearization may, e.g., be predefined by use of a correlation coefficient R2 greater than or equal 0.995.
In some embodiments according to the present invention, the first volume flow is determined as a function of the flow resistance, the second volume flow and the difference between second pressure measurement and first pressure measurement.
In some embodiments according to the present invention, the first volume flow is determined as a function of the flow resistance, the second volume flow and the difference between second pressure measurement and first pressure measurement only then when the first volume flow is small as compared to the second volume flow. The first volume flow is in some embodiments according to the present invention to be regarded as small when it is max. 4% or max. 8% of the second volume flow.
In some embodiments according to the present invention, the functional connection of a pressure loss between first pressure measurement location and a section within the blood treatment module is determined by the factory before the beginning of the blood treatment depending on the second volume flow in the secondary circuit or was determined this way.
In some embodiments according to the present invention, the section within the blood treatment module is its center.
The center of the blood treatment module may relate to the distance of the flow on the side of the primary circuit or secondary circuit.
The first volume flow may hereby be zero or be set to zero.
In some embodiments according to the present invention, the functional connection of a pressure loss between first pressure measurement location and a section within the blood treatment module is determined depending on the second volume flow in the secondary circuit as a function of a pressure loss or it was determined this way. This pressure loss occurs between the first pressure measurement location and the second pressure measurement location and depends on the second volume flow. In this case, the pressure loss due to the flow resistance from the first pressure measurement location to a section within the blood treatment module is extrapolated in order to encompass also the flow resistance which occurs up to the second pressure measurement location. This is normally permissible especially then when both flow sections are equally or similarly structured and therefore comprise equal or similar flow resistances.
In some embodiments according to the present invention, the pressure loss between first pressure measurement location and second pressure measurement location is determined—or was determined at a time before the beginning of the treatment—exclusively or not exclusively, considering the pressure loss between the first pressure measurement location and the second pressure measurement location depending on the second volume flow and the volume flow that transfers in the treatment module from the primary circuit into the secondary circuit as UF rate or transmembrane flow.
The sum of the second volume flow and the volume flow that is transported in the treatment module from the primary circuit into the secondary circuit basically corresponds to the volume flow that flows in the second section, i.e., from the blood treatment module to the second pressure measurement location, provided that the first volume flow is significantly smaller than the second volume flow, e.g., max. 10%. As this volume flow is unrealistically high, however, for determining the flow resistance and thus the pressure loss for the whole distance, i.e., from first to second pressure measurement location, a pressure loss proportion of the first section is deducted. This proportion may be approximately determined by use of the total differential:
            (                        ⅆ                      F                          1              ,              m                                                ⅆ          Q                    )                      (                              Q            BK                    +                      Q            UF                    +                      Q            d                          )            /      2        *      Q    sub  with:    F1,m—pressure loss as function of the volume flow between first pressure measurement location and the center of the blood treatment module;    QBK—second volume flow;    QUF—volume flow which transfers in the blood treatment module from the primary circuit into the secondary circuit; and    Qd—second volume flow less the first volume flow.
In some embodiments according to the present invention, a leakage or a leakage rate, which results from or accompanies differently sized volume flows in the secondary circuit downstream and upstream from the blood treatment module, is determined. For determining this, a functional connection of the following parameters is determined or specified, among which are: the first pressure measurement; the second pressure measurement; the flow resistance between first pressure measurement location and a section within the blood treatment module; the flow resistance between the section within the blood treatment module and the second pressure measurement location; the first volume flow; the second volume flow; and—optionally—a third volume flow. The third volume flow corresponds to a fluid exchange or fluid transfer via a membrane between the primary circuit and the secondary circuit of the blood treatment module.
In certain embodiments according to the present invention, a functional connection is understood as a function, a relationship, a mathematical relationship, a formula or the like.
In some embodiments according to the present invention, the tightness of the secondary circuit against an exterior of the secondary circuit is determined between a first valve upstream from the blood treatment module and a second valve downstream from the blood treatment module. These embodiments encompass closing the first valve and closing the second valve. Subsequently, the fluid system upstream from the first valve and/or downstream from the second valve is impinged with an overpressure. This may, e.g., take place by use of the dialysate pump. Hereby, it is checked or monitored whether the overpressure in the fluid system changes within a predefined time span. Additionally or alternatively, it is checked or monitored whether the overpressure changes or decreases. If a pressure drop or pressure decrease beyond a predefined pressure range is detected, the secondary circuit or its section that is tested for tightness is detected as being leaky. The check for pressure drop may take place by use of the first pressure measurement location and/or by use of the second pressure measurement location.
Optionally, it may be checked or ensured in these embodiments whether the first volume flow is zero. Ensuring that the first volume flow is zero takes place in that, e.g., no flow is generated by the substituate pump.
In some embodiments according to the present invention, a leakage in the secondary circuit is found and the blood treatment apparatus or even only an ultrafiltration is stopped for patient safety reasons if the found pressure drop is outside the predefined pressure range.
In some embodiments according to the present invention, an offset error in determining the volume flow is found when the volume flows of the secondary circuit are differently sized downstream and upstream from the blood treatment module, if the pressure drop is not outside the predefined pressure range. This offset may be included in further measurements and/or be considered for the treatment of the patient without having to interrupt the blood treatment.
In some embodiments according to the present invention, a volume flow upstream and/or a volume flow downstream from the blood treatment module is determined by a pressure difference determination at defined flow resistances.
Such defined or known flow resistances may appear at valves, apertures or other components present in the circuit.
In some embodiments according to the present invention, an offset for the volume flow determinations is determined. This encompasses checking, particularly according to an approach as described above, whether the secondary circuit or a viewed section hereof is tight against an external environment and/or a further line section. It further encompasses checking or ensuring whether or that no fluid between the primary circuit and the secondary circuit, for example, via the blood treatment module, is exchanged. Again further, this procedure encompasses determining a difference between the volume flow upstream and the volume flow downstream from the blood treatment module in the secondary circuit. This may be determined, e.g., according to a method as described above.
Finally, this procedure encompasses setting the difference between the volume flows—or a value correlating herewith—as offset.
In certain embodiments according to the present invention, the method encompasses determining a fluid exchange or fluid transfer—or a value therefor—in the blood treatment module between the primary circuit and the secondary circuit. Such fluid exchange is deemed to be determined when differently sized volume flows in the secondary circuit are found downstream and upstream from the blood treatment module.
Such fluid exchange may be equated to the whole transmembrane flow which basically corresponds to the ultrafiltration rate (UF).
If such fluid exchange is found, it may be checked in a subsequent step whether an offset or a leakage is present. The results of this check are included in the further dialysis treatment by either setting an offset or terminating the treatment of the patient.
In some embodiments according to the present invention, determining the first, second, third and/or fourth pressure measurement is part of the method, in others it is not. Determining the pressure values may take place directly, e.g., by direct measurement, or indirectly. It is therefore called a pressure measurement even then when the pressure is not measured but determined or set otherwise, e.g., by calculating from other quantities.
In certain embodiments according to the present invention, the calculating device comprises or is connected with one or more controlling or regulating units for controlling or regulating a blood treatment apparatus.
In some embodiments according to the present invention, the calculating device is suited and configured for qualitatively determining the first volume flow of the secondary circuit as a proportion of a second volume flow.
In some embodiments according to the present invention, the blood treatment apparatus comprises the devices that are necessary and provided or configured for executing the method according to the present invention. This especially applies for the devices mentioned in relation with the method disclosed herein. A blood treatment device can comprise—as any other device according to the present invention—at least one or more devices suited and/or configured and/or adapted such that one, more or all steps mentioned in here can be executed by the respective device.
In certain embodiments according to the present invention, the fluid connection, which is only optional and provided for introducing the first volume flow from the secondary circuit into the primary circuit, is a line, in particular a tube line or connecting line.
In some embodiments according to the present invention, the fluid connection is and/or comprises no filter membrane.
In some embodiments according to the present invention, the blood treatment apparatus comprises at least or exactly two pressure measurement locations located in the secondary circuit upstream from the blood treatment module and/or after branch-off of the fluid connection from the secondary circuit.
Additionally or alternatively, the blood treatment apparatus comprises in these embodiments two pressure measurement locations located in the secondary circuit downstream from the blood treatment module.
In some of the latter embodiments according to the present invention, each of at least two pressure measurement locations, e.g., the first and the third, or the second and the fourth, are located upstream or downstream from a known flow resistance. Thus, the first and the third pressure measurement location may be located or may measure upstream or downstream from the first valve. Further, the second and the fourth pressure measurement location may be located or may measure upstream or downstream from the second valve.
In certain embodiments according to the present invention, the blood treatment apparatus is a hemofiltration apparatus or a hemodiafiltration apparatus.
In some embodiments according to the present invention, the blood treatment module is a blood filter, a dialysis filter or a hemodialysis filter.
Some, a few or certain embodiments according to the present invention comprise one, some or all of the following advantages:
According to the present invention, there is advantageously no need for an apparatus for measuring the substituate flow or the dialyzer flow directly.
Hemodialysis is a method for removing uremic substances and for removing liquid from the blood of patients that suffer from renal insufficiency. During hemodialysis, the patient's blood is purified outside the body in a dialyzer. The dialyzer comprises a blood chamber and a dialyzing liquid chamber which are separated by use of a semi-permeable membrane. During the treatment, the patient's blood flows through the blood chamber. In order to purify the blood effectively from uremic substances, fresh dialyzing liquid continually flows through the dialyzing liquid chamber.
While in hemodialysis (HD) the transport of the smaller molecular substances through the membrane of the dialyzer is basically determined through the differences in concentration (diffusion) between the dialyzing liquid and the blood, in hemofiltration (HF) substances dissolved in plasma water, in particular substances of higher molecular weight, are effectively removed through a high liquid flow (convection) through the membrane of the dialyzer. In hemofiltration, the dialyzer serves as filter. A combination of both methods is the hemodiafiltration (HDF).
During hemo(dia)filtration, a part of the serum that was removed through the membrane of the dialyzer is replaced by a sterile substitution liquid which generally is supplied to the extracorporeal blood circuit either upstream from the dialyzer or downstream from the dialyzer. The supply of the substitution liquid upstream from the dialyzer is also called “predilution,” the supply downstream from the dialyzer “postdilution.”
The substituate flow may also be determined indirectly. This could be calculated depending on the type of the utilized substituate pump, e.g., indirectly from the rotational speed and the stroke volume of the substituate pump, which may be designed as an occluding tube roller pump, that is dependent on the input pressure. However, the real substituate flow may deviate more or less from the calculated substituate flow due to, e.g., tube kinking or incomplete occlusion of the pump tube and the like. Such errors or deviations between substituate flow that was indirectly determined and actual substituate flow are regularly not to be found through known monitoring methods such as, e.g., TMP monitoring; the accuracy in balancing is not affected with such deviations in TMP monitoring (TMP—transmembrane pressure). The present invention advantageously solves this in some embodiments.
In HDF treatments, the clearance is determined with middle molecules of the substituate flow. Deviations in the substituate flow are thus reflected in the administered dialysis dose of the treatment. The accuracy and the safety of the treatment of the patient may thus advantageously be increased in some embodiments, if the exact substituate flow is known.
An advantage of some embodiments according to the present invention is the accuracy in determining the substituate flow. The achievable accuracy is based, inter alia, on the assumption that the flow resistances R1 and R2 are caused by non-exchangeable hydraulics components of the blood treatment apparatus used for the treatment, which are used for calculating according to the present invention the substituate flow. Thus, the calculation is not based on the flow resistance of disposables that are specifically chosen and used for the individual treatment session (e.g., dialyzers with in part very different ultrafiltration coefficients), the flow differences of which may differ from type to type and even from disposable to disposable of the same type. The achievable accuracy is, inter alia, also based on the assumption that all fluids to be considered with the volume flow determination are fluids the properties of which are known and in addition not changeable. This applies, e.g., for dialysate on which the calculations described herein are based. The same assumption, however, does not also apply for other fluids such as blood. Its viscosity may vary from treatment to treatment due to a changed composition (Hkt, TP, fibrinogen, etc.). Furthermore, viscosity of blood may also change during a treatment due to the water removal. During hemodiafiltration treatments, the effective UF capacity of the dialyzer may additionally change due to the construction of a reversible secondary membrane depending on the substituate rate and the treatment mode (pre-/postdilution). This is advantageously also not an issue in the method according to the present invention.
During the dialysis treatment, the transmembrane flow or the UF rate may constantly be determined by use of the pressure difference measurement and with the previously determined flow resistance measurement. This may also advantageously contribute to increasing patient safety.